The present invention relates to biodegradable polymers or biodegradable polymer compositions having a phenol-containing compound and methods for making such polymers. In a major aspect, phenol-containing compound is included in the biodegradable polymer or biodegradable polymer compositions at an amount sufficient to slow the degradation rate thereof.
From an environmental perspective, biodegradable polymers are an attractive alternative to the more prevalent traditional petroleum-based nonbiodegradable polymers. Biodegradable polymers do not have to be landfilled and thus contribute less to the solid waste problem created now being experienced by society. Further, since biodegradable polymers eventually re-enter normal geochemical cycles over time, they are less likely to become an entrapment or an ingestion hazard to wildlife.
Biodegradation is defined as a process carried out by microbes; e.g., bacteria or fungi, wherein a polymer chain is cleaved via enzymatic activity to form monomers or short chains. Hydrolysis and oxidation arc believed to be the two principal mechanisms by which polymers are degraded. Microbes generally assimilate the monomers or short chains. For example, in an aerobic environment, these monomers or short chains are ultimately oxidized to carbon dioxide, water, and new cell biomass. In an anaerobic environment, the monomers or short chains are ultimately transformed into carbon dioxide, water, acetate, methane, and cell biomass. Efficient biodegradation requires that direct physical contact be established between the biodegradable material and the active microbial population or the enzymes produced by the active microbial population.
Many biodegradable polymers have been developed and are currently used in various plastic products. Cellulose or cellulose derivatives having a low degree of substitution (DS) may be biodegradable under certain conditions. Cellulose can be degraded in the environment by both anaerobic or aerobic microorganisms. Typical endproducts of this microbial degradation include cell biomass, methane, carbon dioxide, water, and other fermentation products. The ultimate endproducts depend upon the type of environment as well as the type of microbial population that is present. Cellulose esters form hard, clear plastics and thus are suitable for eyeglass frames, toys, toothbrush handles, and the like. With the prevalence of cellulose ester materials in consumer products, it is desirable to have the ability to make biodegradable materials therefrom.
Polyhydroxyalkanoates (PHA), such as polyhydroxybutyrate (PHB), polycaprolactone (PCL), or copolymers of polyhydroxybutyrate and polyhydroxyvalerate (PHBV), have been known for at least twenty years. With the exception of polycaprolactone, they arc generally prepared biologically and have been reported to be biodegradable.
U.S. Pat. Nos. 5,480,962 and 5,498,453 to White et al., which are herein incorporated by reference as if fully disclosed herein, describe aliphatic copolyesters having repeat units prepared from succinic and adipic acid, including those containing 1,4-butanediol-derived moieties. These patents indicate that such copolyesters could be used in disposable articles as a result of their propensity to undergo microbial degradation in a composting environment. Examples of appropriate disposable articles in which the aliphatic-copolyesters may be used are food packages, other types of packaging materials, garbage bags, lawn bags, and agricultural mulch films.
U.S. Pat. Nos. 5,292,783, 5,446,079, 5,559,171, 5,580,911, 5,599,858, and 5,900,322, to Buchanan et al., are incorporated by reference as if fully disclosed herein. These patents describe biodegradable polymers, such as aliphatic-aromatic copolyesters, aliphatic polyesters, cellulose esters, blends of cellulose esters and aliphatic-aromatic copolyesters, blends of cellulose esters and aliphatic polyesters, and blends of cellulose esters, aliphatic-aromatic copolyesters, and aliphatic polyesters. Because these polymers are biodegradable in a composting environment, they have utility in a variety of disposable articles, including diapers, sanitary napkins, bed liners, food bags, trash bags, films, and fibers.
Examples of other known biodegradable polymers are poly(vinyl alcohol), poly(ethylene-co-vinyl alcohol), poly(vinyl acetate), and poly(ethylene-co-vinyl acetate). Poly(vinyl alcohol) is a water soluble synthetic polymer that is used extensively in fibers, films, papers, and adhesives. Poly(ethylene-co-vinyl alcohol) is a thermoplastic material commonly used in laminates for food containers due to its excellent film forming and oxygen barrier properties.
Despite the desire to reduce pollution, it may not be feasible to use conventional biodegradable polymers or biodegradable polymer compositions in situations where degradation may start prior to the end of the useful life of the product formed from the biodegradable polymer or biodegradable polymer composition. For instance, people may place biodegradable garbage bags outside of the home several weeks or possibly even months before they are disposed of at a dump site. If the degradation rate of a garbage bag is high enough to result in biodegradation of the plastic bag after only a few weeks of exposure to microbes, the bag could disappear while the garbage is sitting outside. There would then be no way to carry the garbage to a dump site. Even worse, animals looking for food may scatter the garbage all over a person""s yard.
In view of the foregoing, there exists a need to develop a method for slowing the degradation rate of a biodegradable polymer. Such a method would make biodegradable articles more attractive in cases where the article needs to remain intact for a period of time after being exposed to microbes. For example, a person could place garbage in his yard for several weeks without being concerned that the bag containing the garbage might degrade before the garbage can be picked up for dumping.
In one aspect, the invention provides a method for slowing the degradation rate of a biodegradable polymer or biodegradable polymer composition. In another aspect, the invention provides a biodegradable polymer composition comprising a biodegradable polymer or biodegradable polymer-second material composition and a phenol-containing compound mixed therein.
Additional advantages of the invention will be set forth in part in the detailed description, which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of preferred embodiments of the invention, and are not restrictive of the invention, as claimed.